Hello, we are scientists that are a part of the Event Horizon Telescope project.

This telescope array is using Very Long Baseline Interferometry (VLBI) to create a composite image of the event horizon of the black hole, Sagittarius A*. Unlike a photograph – which is composed light hitting a single focal point on an optical lens which is captured by the camera – the EHT project is capturing data from 1.3mm radio wave detections from around the world to create a “virtual mirror” that will help create the first image of a black hole.

Proof or check out this PBS special

Please note that we will begin posting answers at 11am PDT/2pm EDT, as Avery, Dimitrios and I are in meetings/teaching this morning.

About the project:

  • Our group is currently using 9 telescope arrays with locations across the Earth in Mexico, Chile, Hawaii, and Spain

  • 3 other arrays will be incorporated as well, including a location at the South Pole

  • The project is capturing this data on 126 HGST Ultrastar helium-filled 6TB hard drives; currently 756TB of storage with plans to expand to 6PB

  • The hard drives are encased in a custom enclosure of eight drives each that process data at the speed of 64 Mb/sec

  • Each day an observation is run at a site, the site captures 350TB of data

  • 75 Scientists are currently contributing to the project

  • For context, EHT is processing ~10x the amount of data of the Large Hadron Collider in Switzerland

Today, you have three astrophysicists answering your questions:

  • Shep Doeleman, Assistant Director, MIT Haystack Observatory and Astronomer at Smithsonian Astrophysical Observatory

  • Dimitrios Psaltis, Professor of Astronomy and Physics, University of Arizona

  • Avery Broderick, Assistant Professor of Physics and Astronomy, University of Waterloo; Associate Professor, Perimeter Institute for Theoretical Physics

Ask us anything!

Thanks for attending - we're wrapping things up here - we had a ton of fun! To learn a bit more, please see this month's Scientific American:


Comments: 1468 • Responses: 19  • Date: 

rsotoii467 karma

If a black hole swallows only electrons, will the electrical repulsion be eventually greater than the gravitational attraction?

sdoeleman444 karma

This is a very interesting question, and it's true that if a black hole ingested only particles of one charge it could accumulate charge and then repel like charges, but what may happen in reality is that protons or positrons would be attracted to the charged BH and cancel the charge. In other words, BH's are always expected to be neutral.

WafflesWithoutCheese381 karma

How much more can we learn about black holes before we hit the ceiling where we will need to get instruments close to black holes to make further discoveries?

sdoeleman603 karma

A running joke among BH researchers is that we need to send one of us with a laser pointer to the event horizon and then point the laser back to earth. That would give us a lot of info, but also cost us an astronomer (good value?). The EHT will get us closer to the BH and Event Horizon than we have ever been, and in addition to a possible image, we can also trace orbits of material in time, so there are a number of cool experiments that will play out over the next 3-5 years. A lot to keep us occupied, so the ceiling is some ways away!

sacuLSDougan284 karma

You mentioned that this will be able to create the first image of a black hole. All we have now are drawings of we think it looks like. Do you think it will look similar, or completely different than our idea of a black hole?

sdoeleman433 karma

The beauty of the EHT is that we really don't know exactly what we'll see. If we understand the physics and General Relativity, then we can predict what we'll see: a bright ring near the last orbit photons can trace with a dim interior (caused by gravity pulling ferociously on escaping photons coming toward us). Einstein's theory predicts what we should see, but if we see something else (a warped shadow or a completely unexpected shape) then things get very interesting.

Manderson9316181 karma

When will we see these images ?

sdoeleman259 karma

The EHT has already measured the size of the supermassive BH at the center of the Milky Way (and also another at the heart of the Virgo galaxy). Each year we add more telescopes to the global array, filling in the earth-sized 'lens', so our ability to image gets better all the time. In 2017, we'll add ALMA, a huge facility in Chile, and that will enable a really good shot at bringing a BH into focus for the first time.

doctorheredoctor132 karma

If we had a radio telescope on the surface of the Moon, do we currently have the technology and know-how to incorporate that into a super-VLBI?

Bonus: What other kinds of objects will you image with the EHT?

sdoeleman128 karma

Wow! Someone is thinking BIG! We could certainly put a station on the Moon and the resulting magnification factor would be huge - 80,000 times better than Hubble (check me on that). The problem is that this might be too good in that we probably would not have the sensitivity (unless the antenna on the moon was very large) to detect a black hole on such a long baseline. The reason is that there has to be a lot of brightness on very small scales. Also, we'd have to wait a long time before the Moon data could get back to us! We hope to image other galaxies with the EHT - astronomers want to image the high speed jets launched by black holes and those show up in a number of sources. THe EHT will provide the sharpest view of these as well.

pfmonkey54 karma

Was there any particular technologies or engineering challenges you and your team are proud of achieving to bring this project about?

sdoeleman70 karma

Great question. In order to pull this off we had to create new systems that could record radio signal at ultra-high speeds in real time. The EHT works by then bringing these recordings together (later) the same way an optical mirror focuses light. Developing these systems has benefited enormously from Moore's law, so our instruments have leaped ahead in capability, and the increased sensitivity that comes from recording more data was the key to making this work. So the international team is proud of these new purpose-built systems, and going to high altitudes (and being oxygen starved) to get them going.

hoti010148 karma

  • If you capture 350TB of data per day, and you only have an array capable of storing 756TB of data, how do you archive or select only the relevant data?
  • Could you explain how this works like I am 5? I don't quite understand how the array of radio telescopes will allow you to understand the environment around the event horizon. How do you filter out information that isn't near the event horizon? What do you hope to achieve from this study?

sdoeleman58 karma

Ok, good question. The EHT captures data at each site around the world. Our target rate is 8GBytes per second at each site. Over 5 days, and with some down-time for calibration, we need to record about 200TB per day. Over 5 days, that's about 1 PetaByte. When we fill up hard disk drives, we swap them out with empty ones, so we can record as much data as we need to at each site.

The EHT works by combining data from telescope around the world that are all looking at the same black hole at the same time. When combined, the EHT works in a similar way to an optical mirror that merges all the data hitting it at the focus. In this way we use the Earth as a giant mirror and make an image with ultra-high magnification.

luvbitches44 karma

6PB is a lot of storage! How do you guys manage that much data?

sdoeleman84 karma

We have custom enclosures that house 16 disk drives, each at ~6TB, so a total of 96TB. We stripe the data across the drives and then beat any internet by shipping the filled disks via airplane back to a central location for processing.

RoxasV226 karma

  • I watch a lot of astronomy/physics documentaries, do you have any recommendation of an informative documentary?

  • Based on information I have gathered, it is said that black holes actually grow in size when absorbing matter (or fusing with other black holes), is this all observed or mostly theory?

  • Finally a kind of fun question, do you believe every black hole is home to a universe and our own universe is within a black hole?

sdoeleman59 karma

I love the old COSMOS and the new one as well! The event horizon of BHs are predicted to grow as they eat more matter. It's hard to observe this for a single black hole (the time scales are too long), so astronomers do population studies across many black holes to see how big they get over time. It's like an alien looking at the whole population on Earth (babies to older specimens) to study how people age - instead of watching one person grow old.

RockVegas18 karma

Is it possible to not feel like a badass saying "Event Horizon"?

sdoeleman48 karma

No. This is an exciting project - we go to the top of extinct volcanoes with telescopes on top and we lug atomic clocks with us! All we need now are bullwhips and it's Indiana Jones.

JewelCuttersProxy14 karma

Beside needing an understandably absurd amount of storage, what are the other technical computing hurdles you face?

sdoeleman19 karma

Excellent question. We also need to record the data quickly! The challenge is that we use relatively small radio dishes because we observe at high frequencies - and the higher the frequency, the smoother the dish has to be (and it's hard to make large, smooth dishes). So to compensate for the small dishes we need to record huge bandwith (slices of the radio spectrum). So a big hurdle was to develop special systems that can digest data quickly.

inspiredunease8 karma

Presumably you are using custom software for collating, tracking and interpreting the data. What languages/tooling do you use?

sdoeleman11 karma

We typically use Off the Shelf hardware at this point, and develop custom code. At the moment we use C for the number crunching in the cluster that compares data from around the globe, and a variety of languages for the imaging, calibration, modeling: python, C...

robsquad8 karma

as a sophomore undergraduate philosophy major, I've been taking more and more space time and quantum based classes as of late. is there any hope for a philosophy major to make it into an astrophysics grad school program? ...or is preference usually shown for physics majors

sdoeleman24 karma

Many roads lead to astronomy! When I left undergrad I spent an entire year in Antarctica doing a lot of cool(!) research, only some of which was astro-related. It was one of the highlights of my career. I then found ways to use that experience as I moved to astronomy. I also had a friend in graduate school who was a philosophy major and then focused on astronomy - she's very very smart and now teaches at Columbia University - look her up: Janna Levin.

TriTheTree7 karma

How much funding does this project receive? I'm interested in how a project of this undertaking to find out what a black hole looks like is funded.

sdoeleman16 karma

Not enough! The cool thing about the EHT is that we put specialized equipment at existing telescopes to form an entirely new type of telescope (as big as the earth). So in that sense it is huge 'bang for the buck'. We just got a very nice grant from the NSF for $6.5M that covers the build-out (on telescopes that cost over $1Billion) of our EHT equipment. What we need at this stage are resources to speed up data processing and analysis to answer to big questions: was Einstein right? How to BH's feed, and how do they affect their host galaxies.

Electricengineer6 karma

What methods are you using to analyze the data?

sdoeleman10 karma

We use a technique called VLBI: capturing data at radio telescopes that are looking at the same black hole at the same time. We then compare the data from different sites in the same way an optical mirror combines data from a large mirror at the focal point. We play the data back in a large computing cluster (many servers linked together) to do this comparison. The trick is to make an image out of an sparse data set (we don't have telescope all over the globe).

F1r3bird4 karma

If the gravity of a black hole traps protons how can they emit hawking radiation?

And a second question, if the nature of a black hole's gravitational pull makes it unobservable, and we are observing all distortions and radiation coming off them from a very limited scope (read, from earth, around it, and some of space) how do we know that hawking radiation is not a result of mass that passes near to a black hole, rather than coming from it?

thank you for your time

sdoeleman10 karma

The black hole eats anything, including protons, electrons, etc... Hawking radiation is essentially particles coming into existence outside the BH: one falls in and the other escapes, so it isn't protons that are emitting Hawking radiation.

TheeRedaktor3 karma

Does research into black holes have any pragmatic function for society outside of expanding our understanding of our universe?

Edit: presently

sdoeleman9 karma

Great question. It's instructive to ask what answer Einstein might have given to this same question asked about his theory of General Relativity (GR), developed 100 years ago. At that time, there was no space travel, and almost no way to detect any difference between Newtonian and Einsteinian gravity. I don't think he would have been able to come up with anything 'pragmatic'. But of course today we use GR effects everyday: GPS wouldn't work without corrections derived from GR. So the answer is that the payoff from BH research may not be evident now, but if we reveal something fundamental about gravity, the consequences in the future could have high impact. Fundamental science is usually a solid investment.

shiftt2 karma

Why are super massive black holes located at the center of galaxies?

sdoeleman3 karma

Great question and one that many astronomers are working on. Currently we believe the galaxies and black holes evolve together with black holes affecting how galaxies grow, and then the black holes growing as galaxies merge.